The present invention relates generally to automotive vehicles, and more particularly, to a cruise control system.
Cruise control systems are well known in the automotive arts and generally make driving an automotive vehicle easier by automatically adjusting the speed of the vehicle without intervention by the driver. Traditionally, cruise control systems have been designed to maintain a constant speed that is preset by the driver. Thus, in traditional systems, the driver accelerates the vehicle until the vehicle is travelling at the desired speed. The driver then initiates the cruise control by pushing the cruise control button on the steering column or dashboard. Once engaged, the cruise control continuously monitors the speed of the driver""s vehicle and automatically adjusts the speed in order to maintain the preset speed.
While traditional cruise control systems have been widely accepted by automotive drivers, several disadvantages exist. Traditional cruise control systems are generally ineffective when a moderate amount of traffic exists on a roadway. In these situations, the speed of the surrounding vehicles fluctuates more often and with greater variation. Moderate traffic levels also provide less room for the driver to avoid slower and faster moving vehicles. In moderate traffic the driver must adjust the vehicle speed manually without using the cruise control since it is often difficult or impossible to maintain a constant speed.
Another disadvantage arises when a driver wishes to maintain a certain distance with another vehicle. This often occurs when a group of people are travelling together in two or more vehicles. In this situation, the lead vehicle may use a cruise control system to maintain a constant speed. However, the other vehicles encounter difficulties attempting to use traditional cruise control systems to follow the lead vehicle. Traditional cruise control systems usually do not provide precise enough selection of the preset speed to allow one vehicle to match the speed of another vehicle. Another problem is that following drivers are usually unable to visually perceive the exact speed of the lead vehicle. Thus, when drivers try to use traditional cruise control systems to follow a lead vehicle, the following vehicle usually slowly encroaches upon or slowly falls further behind the lead vehicle. As a result, the driver is required to regularly adjust the preset speed of the cruise control system or may choose to manually control the vehicle speed. Following a lead vehicle can also be difficult when the lead vehicle is not using a cruise control system to maintain a constant speed.
Adaptive cruise control (xe2x80x9cACCxe2x80x9d) systems may eliminate these problems by allowing a driver to maintain the same speed as a target vehicle. Accordingly, a driver in a vehicle equipped with ACC (xe2x80x9cthe ACC vehiclexe2x80x9d) typically maneuvers the ACC vehicle behind a lead vehicle (xe2x80x9cthe target vehiclexe2x80x9d) and engages the ACC system. The ACC then tracks the target vehicle and automatically adjusts the speed of the ACC vehicle in order to maintain the distance between the ACC vehicle and the target vehicle.
One problem with current ACC systems is that the ACC usually has trouble tracking the target vehicle along curves in the road. Typically, ACC systems are designed to travel at the preset speed when no target vehicle exists directly ahead of the ACC vehicle. This is often called CC mode (Conventional Cruise Control), while the tracking function is called ACC mode. An ACC will change from the ACC mode to the CC mode when the target vehicle changes lanes out of the lane of the ACC vehicle. When the ACC disengages, the cruise control system typically selects a preset speed chosen either by the manufacturer or the driver and maintains the speed of the vehicle at the preset speed. Therefore, when the target vehicle changes lanes away from the ACC vehicle, the ACC disengages and the vehicle maintains a preset speed.
When the target vehicle remains in the same lane as the ACC vehicle and instead enters a curve in the road, the ACC desirably continues tracking the target vehicle and maintaining the same speed as the target vehicle. However, there are no effective methods to distinguish between the cases of a lane change and curve travel by the target vehicle. Usually, current ACCs determine that the preceding vehicle has changed lanes. After the ACC vehicle enters the curve, the ACC then determines that the preceding vehicle is a target. Namely, the mode of the ACC switches as follows: first ACC mode, next CC mode, then ACC mode. Desirably, however, the ACC vehicle should remain in the ACC mode during the entire curve travel.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the embodiments described below include an ACC system for deciding whether a target vehicle is traveling along a curve or whether the target vehicle is changing lanes. The ACC measures an azimuth angle and a relative velocity between the ACC vehicle and the target vehicle. After the target vehicle enters the curve or starts the lane change, the relative velocity and the azimuth angle starts changing. The temporal locus is remarkably different between the two possibilities since the change in velocity and azimuth angle is different for each possibility. When the angle is getting larger than 1.5 degrees, the ACC starts judging whether the preceding vehicle is entering a curve or changing lanes. The judgment can be made by comparing several locus patterns of the preceding vehicle during curve travel and lane changes.